This invention relates to a hydraulic damper of adjustable damping force type and, particularly, to a control system for controlling the damping force of the hydraulic dampers of aforesaid type for use in a vehicle.
Various proposals have been made with respect to a hydraulic damper of adjustable damping force type which, when being incorporated on a vehicle such as an automobile, enables the damping force to be changed in accordance with the driving conditions of the vehicle and the conditions of the road, thereby improving comfort and safety in driving the vehicle and improving the steering characteristics.
In general, a vehicle usually has a plurality of hydraulic dampers corresponding in number to the wheels of the vehicle, each of the dampers including a damping force producing mechanism; a damping force adjustment member for adjusting the effective passage area of an oil passage in the damping force producing mechanism; an actuator connected to the damping force adjustment member; and an electric power supply circuit for supplying electric power to the actuator. The damping force producing mechanism is provided with a conductive disc having a notch in a portion thereof which is rotationally driven by the actuator, and a plurality of brushes for controlling the operation of the actuator and indicating the selected damping force in accordance with the conductive conditions between the brushes and the disc. The brushes usually contact the disc and, when the brushes face the notch of the disc, they are not in contact.
In the conventional damping force producing mechanism described above, if a malfunction condition such that any of the brushes is shorted-circuit occurs, it is impossible for the damping force to be selected.